As image recording and display apparatuses have higher functions, image forming apparatuses such as color copying machines, color printers, and the like have prevailed, and a color facsimile has been developed as an image communication apparatus.
The communication scheme for the color facsimile is standardized as ITU-T recommendations, and T.30, T.4, T.42, and T.81 have been recommended. Color image encoding adopts JPEG (Joint Photographic Experts Group) of the T.81 recommendation.
In the T.30 recommendation, monochrome image reception performance (to be referred to as “monochrome reception performance” hereinafter) is indispensable, but color image reception performance (to be referred to as “color reception performance” hereinafter) is optional. Even when the sender wants to send a color image, if the receiver does not have color reception performance, it cannot send a color image. Therefore, when the user makes color image transmission operation, if the receiver does not have color reception performance and the communication is interrupted, the communication cost is wasted, and the user must re-send a monochrome image. When the receiver does not have color reception performance, if a color image to be sent is converted into a monochrome image, the monochrome image is sent against user's intention.
In a memory transmission mode in which a color image is saved in a memory, and then begins to be sent, color image data compressed by JPEG is normally saved in the memory to improve the use efficiency of the memory. If the receiver to which that image is to be sent does not have color reception performance, a process for converting the image into a monochrome image must be done. That is, the saved JPEG image data is expanded to, e.g., multi-valued RGB data, which is binarized by error diffusion or dithering. Furthermore, the binary image is compressed by an encoding scheme such as MH (Modified Huffman), MR (Modified READ), MMR (Modified Modified READ), JBIG (Joint Binary Image Group), or the like in accordance with the reception performance of the receiver. These processes require a speed corresponding to the communication rate, resulting in high cost since hardware components must be added and performance must be improved.
Upon sending a facsimile document, e.g., upon sending a document which includes both color and monochrome image pages (to be referred to as a color/monochrome mixed document” hereinafter) (e.g., a monochrome image is sent as the first page, and a color image is sent as the second page), the first monochrome image page can be sent irrespective of the presence/absence of color reception performance of the receiver, but the second color image page cannot be sent if the receiver has no color reception function. As a result, the receiver receives the first page alone, and both parties may be confused.